This invention relates generally to incandescent lamps and, more particularly, to automotive turn signals and other such lamps used to provide an amber color when illuminated.
Amber colored incandescent lamps are used in automotive exterior lighting applications for such things as turn signals, parking lights, and marker lamps. These lamps produce a distinctive color that, in conjunction with the white light from headlamps and the red light from tail lamps and other such rearwardly-directed lighting, helps other drivers and pedestrians in quickly determining the orientation of the vehicle. Amber bulbs can also be used within the vehicle as indicator lamps and can be used in other diverse applications as well.
For purposes of automotive exterior lighting, the United States and certain other countries and regions have adopted regulations concerning the required spectral content for these amber lamps. These regulations help insure that the color of the emitted light has the distinctiveness desired to easily differentiate it from white and other colored light. Traditionally, the glass and/or glass coating used to produce these lamps have used cadmium as a coloring agent. However, as is known, the use of cadmium raises environmental concerns and has been classified as a toxic material. Consequently, various cadmium-free amber coatings have been developed that are applied to the surface of a standard borosilicate glass lamp. With these coatings can come various other problems, however. For example, some coatings reflect infrared light emitted by the filament back into the bulb, resulting in overheating of the bulb and a concomitant shortening of the bulb life. Other coatings fade or flake off as a result of the heat generated by the lamp. As a result, the use of cadmium-based amber lamps is still commonplace within the automotive industry.
More recently, newer coating technologies have begun to appear that are reputed to provide an amber color that meets SAE and ECE guidelines while avoiding the above-noted problems of more traditional cadmium-free coatings. While perhaps suitable for their intended purpose, these coatings nonetheless still involve the use of additional materials and processing steps that increase the overall cost of manufacturing the lamp.
It is therefore an object of this invention to provide an automotive lamp made from a cadmium-free glass that does not require a special coating to achieve the desired amber color.
In accordance with the invention, there is provided an automotive lamp that comprises a sealed envelope having a filament or other light emitting element contained therein, with the envelope being formed from a barium-silicate based glass that is essentially free of cadmium and that comprises barium oxide in the range of 2.15%-2.25% by weight and strontium oxide in the range of 5.58%-5.82% by weight. Preferably, the glass further comprises potassium oxide in the range of 8.9%-9.3% by weight and molybdenum oxide in the range of 0.068%-0.072%. Even more preferably, the glass consists essentially of the following elements in amounts that are within 2% of the following weight percentages:
The lamp so constructed can provide an amber color that meets SAE and ECE colorimetry requirements for exterior vehicle lamps without the use of cadmium or special coatings. The envelope can be formed into a wedge base lamp to produce GT-8 and other industry-standard lamps.
In accordance with another aspect of the invention, a method of manufacturing an automotive lamp is provided using glass having the composition given above. The method uses a segment of glass tube having the above-noted composition. First, one end of the glass tube is softened using heat and then blown into a globe using a mold. Then, a light emitting element is inserted into the other end of the glass tube. Finally, a sealed envelope is formed containing the light emitting element, and this is done by softening that other end of the glass tube using heat and sealing that other end by melting of the glass together with the light emitting element contained inside.